Vol. VII, No. 4

February, 1995

Hammers and Nails

by H. Eiteljorg, II

"If your only tool is a hammer, all your problems tend to look like nails."

Although I cannot find the source of that aphorism or even be sure of the exact wording, it is wonderfully apt when thinking about computer use in archaeology. We use the tools we know and understand, sometimes despite the fact that they are not the best ones for the job. Indeed, in the case of computer tools, there are so many available that none of us is really well-versed in the use of all, probably not expert in the use of more than one or two. So it can be difficult even to know which tools are most appropriate, much less how to put them to use.

Some scholars have used spreadsheets as database systems. That is a good example of using one tool when another would do the job better. In place of a simple database system, a spreadsheet is not a bad choice, but sophisticated database management systems offer so much more capability than spreadsheets that even the most modern of spreadsheets cannot compete.

Computer-aided design software (CAD) and Geographic information systems (GIS) are even more likely to be confused. Both are often thought of as graphics programs, and their features seem similar. However, CAD and GIS are quite distinct, because they have been designed to deal with completely different problems. GIS software provides computerized mapping and analyses based on map information (see CSA Newsletter Vol. 5, no. 4, for a fuller description of GIS) (1) ; CAD is computerized drafting and design for architecture and product design. These roots create important differences in the resulting software.

GIS technology descends directly from mapping needs and traditions. Map makers have never just drawn what is there; they have drawn what is of interest for one reason or another -- roads or mountains or harbors. Today, however, what is of interest is much more than geographic features or political boundaries. We want maps showing where there are low levels of pollution or steep terrain or little risk of flooding -- or high concentrations of identified archaeological sites. GIS software makes it possible to draw such maps on demand, and, better yet, to combine seemingly unrelated types of information so that, for instance, we could generate a map showing where archaeological sites are uncommon, the terrain is neither too flat nor too hilly, public services are nearby, and the likelihood of flooding is low; then development could be encouraged there.

A key element of GIS software is that it is designed to deal with bounded portions of the earth's surface. The aim is to show, on a map, areas that meet complex search criteria. As in the example above, the end result of GIS work is normally a map with an area or areas designated as those having the specified characteristics. As a result, GIS software is principally concerned with two dimensions, latitude and longitude or x and y, not elevations. Elevations are treated as information about an area or point, not as parts of the defining geometry.

GIS programs can display three-dimensional maps or terrain models, but they cannot represent well the objects in or on the terrain. Such objects are simply not the focus of the systems.

CAD programs were developed for architects and engineers to deal with objects; indeed, programs were separately developed for the two sets of users. Engineers' three-dimensional creations demanded fully three-dimensional models; so computer-aided design software for engineers uses three-dimensional data for all points in the model. Furthermore, realistic representations of models require that the models contain information about surfaces (and solid objects for some purposes).

Architects, on the other hand, were less concerned about three-dimensional views at the outset. They had relied on plans and elevations for most of their work. They were, however, accustomed to drawing complex buildings with the base drawn on paper and transparent overlays used for different parts of the design, e.g., wiring, plumbing, heating and air conditioning. That feature was incorporated in computer-aided drafting systems for architects; drawings could be broken into parts, and the parts displayed in any combination.

Modern CAD systems contain the important elements of both computer-aided drafting and computer-aided design software. The programs permit fully three-dimensional modeling of objects, large or small, and they permit users to divide models into small pieces according to relevant criteria. In addition, database information can be attached to objects in the model.

Although CAD systems are very sophisticated, they are not well suited for all kinds of analysis. In particular, the software is designed to represent objects, simple or complex, not areas that are independent of those objects. GIS software, on the other hand, is intended to deal with areas, not objects.

CAD and GIS technologies are moving together; both the program operations and the associated data are becoming more similar. But they have not merged and are unlikely to do so for some time yet. At the moment, CAD systems are excellent for modeling three-dimensional material -- small objects, buildings, or excavations -- and for attaching data to objects. Geographic Information Systems are excellent for dealing with terrain, surface survey data, and other information about bounded areas. But neither system is appropriate for all problems; choosing the correct tool requires careful analysis of the problem to be solved.

For other Newsletter articles concerning the use of electronic media in the humanities, consult the Subject index.

Next Article: Pseira CAD Work Continues

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